2
that this is a temporary desktop
That sounds like a bug that is already fixed.
After checking this forum. I find the last Avast program update was 7 days ago
No, it was not. Last update was (iirc) 2 days ago. You will not see it in the history list or by looking at the version number as they where micro-update/micro-fixes.

Not saying it is, but the problems can have to do with the updates MS rolled out recently.
Perhaps the combination of both the MS updates and the avast updates has caused the problems.

Unless you have something like logs that have (at least) a indication, it is mostly hard to tell if not impossible what was causing the problems.
There are really a lot of possible causes.
Even a real tiny hiccup (even if it was less the then a millisecond) in the power can have caused it.